The present invention relates to a catalytic cracking process for heavy oil, in more detail relates to a process for catalytic cracking a low-grade heavy oil containing large amounts of metals such as vanadium, nickel, iron and the like in the presence of a mixture of crystalline aluminosilicate-containing cracking catalyst particles and alumina particles.
The catalytic cracking process for hydrocarbon oil aiming at the production of gasoline has customarily been carried out by using a cracking catalyst which comprises dispersing a crystalline aluminosilicate zeolite in a matrix. This catalytic cracking process has obtained good results seemingly, so far as the hydrocarbon oil containing relatively small amounts of metal contaminants is used as feed oil, even though said feed oil is a heavy oil. However, petroleum conditions have recently gotten worse to bring about a critical situation that a low-grade heavy oil containing large amounts of metals such as vanadium, nickel, iron and the like per se must be subjected to catalytic cracking. So far as said low-grade heavy oil is treated, the usual catalytic cracking process as aforesaid does not necessarily achieve good results.
That is, when the low-grade heavy oil containing large amounts of metal contaminants is treated by using the usual crystalline aluminosilicate-containing cracking catalyst, not only the cracking activity of the catalyst is harmed due to metal deposit but also contaminants increase for promoting dehydrogenation, whereby hydrogen and coke increase and thus the yield of gasoline lowers. And, as the amounts of metals deposited on the catalyst increase, there is even a possibility that the crystalline aluminosilicate zeolite gives rise to crystal breaking and the cracking activity is further deteriorated.
In view of this, as the measures for catalytic cracking of the heavy oil containing large amounts of metals there have usually been employed the process which comprises increasing the amount of cracking catalyst usage in order to lower the amounts of metals deposited on each catalyst particle; or comprises mixing the used cracking catalyst whose amounts of metals deposited are relatively small; and further the process which comprises adding an antimony compound to the feed oil in order to prevent the activity of the cracking catalyst from lowering due to metal deposit. However, these usual processes are not necessarily praiseworthy because the operating cost is expensive. And, it is not preferable to increase the content of crystalline aluminosilicate zeolite in the catalyst for the purpose of increasing the cracking activity, because it leads to promotion of by-production of coke and gaseous components and reduction of the gasoline yield.